@article{sowers_ward_english_nemanich_2000, title={Measurement of field emission from nitrogen-doped diamond films}, volume={9}, ISSN={["1879-0062"]}, DOI={10.1016/S0925-9635(00)00304-6}, abstractNote={This study explores issues related to the measurement of the field emission properties of nitrogen-doped diamond grown by microwave plasma chemical vapor deposition (CVD). Growth conditions have been optimized to produce films with a low concentration of sp2-bonded carbon which results in high electrical resistance. Field emission characteristics were measured in an ultrahigh vacuum with a variable distance anode technique. For samples grown with gas phase [N]/[C] ratios less than 10, damage from micro-arcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured prior to an arcing event. The occurrence of a micro-arc is related to the film properties. The measurements indicate relatively high threshold fields (>100 V μm−1) for electron emission.}, number={9-10}, journal={DIAMOND AND RELATED MATERIALS}, author={Sowers, AT and Ward, BL and English, SL and Nemanich, RJ}, year={2000}, pages={1569–1573} }
 @article{ward_hartman_hurt_tracy_davis_nemanich_2000, title={Schottky barrier height and electron affinity of titanium on AIN}, volume={18}, ISSN={["1071-1023"]}, DOI={10.1116/1.1303733}, abstractNote={Approximately 100 or 1000 Å of AlN was deposited on the (0001)Si-face of on-axis n-type 6H–SiC. The surfaces were examined by ultraviolet photoemission spectroscopy (UPS) utilizing the He I α (21.2 eV) and the He II α (40.8 eV) excitation. Experimental difficulties are discussed. Titanium was deposited on the clean surface of in situ grown AlN. The titanium–AlN interface was also characterized with UPS. Two approaches are presented to identify the valence band maximum (VBM) and the electron affinity χ of the clean surface of AlN was found to be either 0 to 1 eV depending upon the position of the valence band edge. The same assumptions were applied to the analysis of the Ti/AlN interface and, for the case of χ=0 eV, the position of the valence band maximum is 3.4 eV below the position of the Fermi level. For the case of χ=1 eV, the position of the valence band maximum is 4.4 eV below the position of the Fermi level. Therefore, the p-type Schottky barrier height of titanium on AlN is measured to be 3.4±0.2 or 4.4±0.2 eV for χ=0 eV and χ=1 eV, respectively. Independent of the selection of the valence band maximum, the observed Schottky barrier differed from that predicted by the Schottky–Mott model by 1.5±0.2 eV.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B}, author={Ward, BL and Hartman, JD and Hurt, EH and Tracy, KM and Davis, RF and Nemanich, RJ}, year={2000}, pages={2082–2087} }
 @article{sowers_ward_english_nemanich_1999, title={Field emission properties of nitrogen-doped diamond films}, volume={86}, ISSN={["1089-7550"]}, DOI={10.1063/1.371316}, abstractNote={This study explores the field emission properties of nitrogen-doped diamond grown by microwave plasma chemical vapor deposition. Over 70 nitrogen-doped diamond samples were grown on silicon and molybdenum under varying process conditions. Under certain conditions, films can be grown which exhibit photoluminescence bands at 1.945 and 2.154 eV that are attributed to single substitutional nitrogen. Photoelectron emission microscopy with UV free electron laser excitation indicated a 0 or negative electron affinity. Field emission characteristics were measured in an ultrahigh vacuum with a variable distance anode technique. For samples grown with gas phase [N]/[C] ratios less than 10, damage from microarcs occurred during the field emission measurements. Samples grown at higher [N]/[C] content could be measured prior to an arcing event. Contrary to other reports on nitrogen-doped diamond, these measurements indicate relatively high threshold fields (>100 V/μm) for electron emission. We suggest that the nitrogen in these films is compensated by defects. A defect-enhanced electron emission model from these films is discussed.}, number={7}, journal={JOURNAL OF APPLIED PHYSICS}, author={Sowers, AT and Ward, BL and English, SL and Nemanich, RJ}, year={1999}, month={Oct}, pages={3973–3982} }
 @article{nemanich_english_hartman_sowers_ward_ade_davis_1999, title={Imaging electron emission from diamond and III-V nitride surfaces with photo-electron emission microscopy}, volume={146}, ISSN={["0169-4332"]}, DOI={10.1016/S0169-4332(99)00021-5}, abstractNote={Wide bandgap semiconductors such as diamond and the III–V nitrides (GaN, AlN, and AlGaN alloys) exhibit small or even negative electron affinities. Results have shown that different surface treatments will modify the electron affinity of diamond to cause a positive or negative electron affinity (NEA). This study describes the characterization of these surfaces with photo-electron emission microscopy (PEEM). The PEEM technique is unique in that it combines aspects of UV photoemission and field emission. In this study, PEEM images are obtained with either a traditional Hg lamp or with tunable UV excitation from a free electron laser. The UV-free electron laser at Duke University provides tunable emission from 3.5 to greater than 7 eV. PEEM images of boron or nitrogen (N)-doped diamond are similar to SEM of the same surface indicating relatively uniform emission. For the N-doped samples, PEEM images were obtained for different photon energies ranging from 5.0 to 6.0 eV. In these experiments, the hydrogen terminated surface showed more intense PEEM images at lower photon energy indicating a lower photothreshold than annealed surfaces which are presumed to be adsorbate free. For the nitrides, the emission properties of an array of GaN emitter structures is imaged. Emission is observed from the peaks, and relatively uniform emission is observed from the array. The field at the sample surface is approximately 10 V/μm which is sufficient to obtain an image without UV light. This process is termed field emission electron microscopy (FEEM).}, number={1-4}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and English, SL and Hartman, JD and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1999}, month={May}, pages={287–294} }
 @article{wolfe_hinds_wang_lucovsky_ward_xu_nemanich_maher_1999, title={Thermochemical stability of silicon-oxygen-carbon alloy thin films: A model system for chemical and structural relaxation at SiC-SiO2 interfaces}, volume={17}, ISSN={["0734-2101"]}, DOI={10.1116/1.581745}, abstractNote={Alloy thin films of hydrogenated silicon–oxygen–carbon (Si,C)Ox x<2, were deposited and analyzed in terms of changes in structure and bonding as a function of rapid thermal annealing between 600 and 1100 °C using a combination of Fourier transform infrared spectroscopy, Raman scattering and high-resolution transmission electron microscopy. Results showed that three structural/chemical transformations took place upon annealing. The initial reaction (600–800 °C) involved the loss of hydrogen bonded to both silicon and carbon. At intermediate temperatures (900–1000 °C) a Si–O–C type bond was observed to form, and subsequently disappear after annealing to 1050 °C. The formation of ordered amorphous-SiC regions, nanocrystalline-Si regions, and stoichiometric, thermally relaxed SiO2 accompanied the disappearance of the Si–O–C bond at the 1050 °C annealing temperature. Using this alloy as a model system, important information is obtained for optimized processing of SiC–SiO2 interfaces for device applications.}, number={4}, journal={JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS}, author={Wolfe, DM and Hinds, BJ and Wang, F and Lucovsky, G and Ward, BL and Xu, M and Nemanich, RJ and Maher, DM}, year={1999}, pages={2170–2177} }
 @article{nemanich_baumann_benjamin_english_hartman_sowers_ward_1998, title={Characterization of electron emitting surfaces of diamond and III-V nitrides}, volume={8}, number={4}, journal={Diamond Films and Technology}, author={Nemanich, R. J. and Baumann, P. K. and Benjamin, M. C. and English, S. L. and Hartman, J. D. and Sowers, A. T. and Ward, B. L.}, year={1998}, pages={211–223} }
 @article{ward_nam_hartman_english_mccarson_schlesser_sitar_davis_nemanich_1998, title={Electron emission characteristics of GaN pyramid arrays grown via organometallic vapor phase epitaxy}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368775}, abstractNote={Selective growth of arrays of silicon-doped GaN (Si:GaN) pyramids for field emitter applications has been achieved. The electron emission characteristics of these arrays has been measured using techniques such as field emission, field emission energy distribution analysis (FEED), photoemission electron microscopy (PEEM), and field emission electron microscopy (FEEM). The field emission current–voltage (I–V) results indicate an average threshold field as low as 7 V/μm for an emission current of 10 nA. It is suggested that the low threshold field value is a consequence of both the low work function of Si:GaN and the field enhancement of the pyramids. The results of the FEEM and FEED measurements indicate agreement with the field emission I–V characteristics. The FEED results indicate that the Si:GaN pyramids are conducting, and that no significant ohmic losses are present between the top contact to the array and the field emitting pyramids. The PEEM and FEEM images show that the emission from the arrays is uniform over a 150 μm field of view.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ward, BL and Nam, OH and Hartman, JD and English, SL and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Nemanich, RJ}, year={1998}, month={Nov}, pages={5238–5242} }
 @article{nemanich_baumann_benjamin_nam_sowers_ward_ade_davis_1998, title={Electron emission properties of crystalline diamond and III-nitride surfaces}, volume={130}, ISSN={["0169-4332"]}, DOI={10.1016/s0169-4332(98)00140-8}, abstractNote={Wide bandgap semiconductors have the possibility of exhibiting a negative electron affinity (NEA) meaning that electrons in the conduction band are not bound by the surface. The surface conditions are shown to be of critical importance in obtaining a negative electron affinity. UV-photoelectron spectroscopy can be used to distinguish and explore the effect. Surface terminations of molecular adsorbates and metals are shown to induce an NEA on diamond. Furthermore, a NEA has been established for epitaxial AlN and AlGaN on 6H–SiC. Field emission measurements from flat surfaces of p-type diamond and AlN are similar, but it is shown that the mechanisms may be quite different. The measurements support the recent suggestions that field emission from p-type diamond originates from the valence band while for AlN on SiC, the field emission results indicate emission from the AlN conduction band. We also report PEEM (photo-electron emission microscopy) and FEEM (field electron emission microscopy) images of an array of nitride emitters.}, number={1998 June}, journal={APPLIED SURFACE SCIENCE}, author={Nemanich, RJ and Baumann, PK and Benjamin, MC and Nam, OH and Sowers, AT and Ward, BL and Ade, H and Davis, RF}, year={1998}, month={Jun}, pages={694–703} }
 @article{ronning_banks_mccarson_schlesser_sitar_davis_ward_nemanich_1998, title={Structural and electronic properties of boron nitride thin films containing silicon}, volume={84}, ISSN={["0021-8979"]}, DOI={10.1063/1.368752}, abstractNote={The incorporation of silicon into boron nitride films (BN:Si) has been achieved during ion beam assisted deposition growth. A gradual change from cubic boron nitride (c-BN) to hexagonal boron nitride (h-BN) was observed with increasing silicon concentration. Ultraviolet photoelectron spectroscopy, field emission, and field emission electron energy distribution experiments indicated that the observed electron transport and emission were due to hopping conduction between localized states in a band at the Fermi level for the undoped c-BN films and at the band tails of the valence band maximum for the BN:Si films. A negative electron affinity was observed for undoped c-BN films; this phenomenon disappeared upon silicon doping due to the transformation to h-BN. No shift of the Fermi level was observed in any BN:Si film; thus, n-type doping can be excluded.}, number={9}, journal={JOURNAL OF APPLIED PHYSICS}, author={Ronning, C and Banks, AD and McCarson, BL and Schlesser, R and Sitar, Z and Davis, RF and Ward, BL and Nemanich, RJ}, year={1998}, month={Nov}, pages={5046–5051} }
 @article{baumann_bozeman_ward_nemanich_1997, title={Characterization of metal-diamond interfaces: Electron affinity and Schottky barrier height}, volume={6}, ISSN={["0925-9635"]}, DOI={10.1016/S0925-9635(96)00601-2}, abstractNote={In this study, the electron affinity and Schottky barrier height of thin Cu and Zr films on diamond (100) substrates were correlated by means of UV photoemission spectroscopy (UPS) measurements. Prior to metal deposition the diamond crystals were cleaned by a 1150°C or 500°C anneal in UHV, and the surfaces were characterized by AES and AFM. This resulted in surfaces terminated with oxygen or free of chemisorbed species. By means of UPS it was found that whether a metal did induce a negative electron affinity (NEA) on a diamond surface was dependent on the surface preparation before metal deposition and on the metal work function. In particular, the Schottky barrier height for clean surfaces was lower than for surfaces terminated by oxygen. Metal-diamond interfaces exhibiting a NEA had a lower Schottky barrier height than those exhibiting a positive electron affinity. These effects were attributed to different interfacial layers. Field emission measurements were performed before and after metal deposition. For all cases a reduction in the threshold electric field was observed upon metal overgrowth.}, number={2-4}, journal={DIAMOND AND RELATED MATERIALS}, author={Baumann, PK and Bozeman, SP and Ward, BL and Nemanich, RJ}, year={1997}, month={Mar}, pages={398–402} }
 @article{nam_bremser_ward_nemanich_davis_1997, title={Growth of GaN and Al0.2Ga0.8N on patterened substrates via organometallic vapor phase epitaxy}, volume={36}, ISSN={["0021-4922"]}, DOI={10.1143/JJAP.36.L532}, abstractNote={ 
   The selective growth of GaN and  Al0.2Ga0.8N has been achieved on stripe and circular patterned    GaN/AlN/6H-SiC(0001) multilayer substrates. Growth morphologies on the stripe patterns were a    function of the widths of the stripes and the flow rate of triethylgallium. No ridge growth was    observed along the top edges of the truncated stripe patterns. Smooth (0001) top facets formed on    stripes ≥5 µ m wide. Uniform hexagonal pyramid arrays of undoped GaN and Si-doped GaN    were successfully grown on 5 µ m circular patterns. Field emission measurements of a Si-doped    GaN hexagonal pyramid array exhibited a turn-on field of 25  V/µ m for an emission current of 10.8 nA at an anode-to-sample distance of 27 µ m. 
   }, number={5A}, journal={JAPANESE JOURNAL OF APPLIED PHYSICS PART 2-LETTERS & EXPRESS LETTERS}, author={Nam, OH and Bremser, MD and Ward, BL and Nemanich, RJ and Davis, RF}, year={1997}, month={May}, pages={L532–L535} }
 @article{sowers_christman_bremser_ward_davis_nemanich_1997, title={Thin films of aluminum nitride and aluminum gallium nitride for cold cathode applications}, volume={71}, DOI={10.1063/1.120052}, abstractNote={Cold cathode structures have been fabricated using AlN and graded AlGaN structures (deposited on n-type 6H-SiC) as the thin film emitting layer. The cathodes consist of an aluminum grid layer separated from the nitride layer by a SiO2 layer and etched to form arrays of either 1, 3, or 5 μm holes through which the emitting nitride surface is exposed. After fabrication, a hydrogen plasma exposure was employed to activate the cathodes. Cathode devices with 5 μm holes displayed emission for up to 30 min before failing. Maximum emission currents ranged from 10–100 nA and required grid voltages ranging from 20–110 V. The grid currents were typically 1 to 104 times the collector currents.}, number={16}, journal={Applied Physics Letters}, author={Sowers, A. T. and Christman, J. A. and Bremser, M. D. and Ward, B. L. and Davis, R. F. and Nemanich, R. J.}, year={1997}, pages={2289–2291} }